Image forming apparatus, method of adjusting image positional deviation, and computer program product

1. An image forming apparatus comprising: a conveying unit that conveys a recording medium; a movable body that includes a recording head to eject a liquid droplet for image recording to the recording medium, and is supported movably in a main-scanning direction orthogonal to a conveying direction of the recording medium; a movable-body drive unit that moves the movable body in the main-scanning direction; an adjustment-pattern recording controller configured to cause a plurality of adjustment patterns to be recorded with a predetermined edge interval in the main-scanning direction by causing the liquid droplet ejected from the recording head to land on the recording medium, while causing the movable-body drive unit to move the movable body in the main-scanning direction; a reading unit that is mounted on the movable body to irradiate the recording medium on which the adjustment patterns are recorded with read light and read the adjustment patterns by photoelectrically converting reflected light from the recording medium; a calculator configured to calculate a positional deviation correction amount for correcting a deviation of a landing position of the liquid droplet, which is ejected from the recording head and landed on the recording medium, based on an ideal interval between the adjustment patterns recorded on the recording medium and a read result of the adjustment patterns read by the reading unit; a correction unit configured to cause the adjustment-pattern recording controller to record the adjustment pattern at a recording position where the interval between the adjustment patterns becomes an integral multiple of a fluctuation cycle in a relative movement of the reading unit and the adjustment pattern, which is caused by movement of the movable body mounted with the reading unit, and correct the recording position of the adjustment pattern based on the positional deviation correction amount calculated by the calculator; and an ejection timing adjustment unit configured to adjust an ejection timing of the liquid droplet by the recording head by performing repeatedly at least twice a recording process of the adjustment pattern on the recording medium by the adjustment-pattern recording controller, a reading process of the adjustment patterns by the reading unit, a calculation process of the positional deviation correction amount by the calculator, and a correction process of the recording position of the adjustment pattern by the correction unit.

2. The image forming apparatus according to claim 1 , wherein the calculator calculates the interval between the adjustment patterns based on a theoretical speed of the movable body and the adjustment pattern that are relatively respectively moved by the movable-body drive unit and the conveying unit, and an arrival time interval from reading of an edge of a first adjustment pattern to reading of an edge of a second adjustment pattern or an arrival time interval from reading of a center of the first adjustment pattern to reading of a center position of the first adjustment pattern from a center position of the second adjustment pattern.

3. The image forming apparatus according to claim 2 , wherein the adjustment-pattern recording controller causes the recording head to record, as the adjustment pattern, a linear adjustment pattern having a predetermined width and extending over a predetermined length in a sub-scanning direction with a predetermined angle.

4. The image forming apparatus according to claim 3 , wherein the reading unit irradiates the recording medium with the read light having a spot diameter of a predetermined size, and the adjustment-pattern recording controller causes the recording head to record the linear adjustment patterns with a line width and a pattern interval being equal to or larger than the spot diameter of the read light.

5. The image forming apparatus according to claim 1 , wherein the adjustment-pattern recording controller causes the recording head to record, as the adjustment patterns, reference patterns and patterns to be measured to be recorded with an equal interval, the patterns to be measured being recorded under an ejection condition of the liquid droplet different from an ejection condition of the reference patterns.

6. A method of adjusting an image positional deviation, comprising: conveying a recording medium; moving a movable body in a main-scanning direction orthogonal to a conveying direction of the recording medium, the movable body including a recording head to eject a liquid droplet for image recording to the recording medium and being supported movably in the main-scanning direction; recording a plurality of adjustment patterns with a predetermined edge interval in the main-scanning direction by causing the liquid droplet ejected from the recording head to land on the recording medium, while moving the movable body in the main-scanning direction; reading, by a reading unit mounted on the movable body, the adjustment patterns by irradiating the recording medium on which the adjustment patterns are recorded with read light and photoelectrically converting reflected light from the recording medium; calculating a positional deviation correction amount for correcting a deviation of a landing position of the liquid droplet, which is ejected from the recording head and landed on the recording medium, based on an ideal interval between the adjustment patterns recorded on the recording medium and a read result of the adjustment patterns read at the reading; correcting that includes recording the adjustment pattern at a recording position where the interval between the adjustment patterns becomes an integral multiple of a fluctuation cycle in a relative movement of the reading unit and the adjustment pattern, which is caused by movement of the movable body mounted with the reading unit, and correcting the recording position of the adjustment pattern based on the positional deviation correction amount calculated at the calculating; and adjusting an ejection timing of the liquid droplet by the recording head by performing repeatedly at least twice the recording, the reading, the calculating, and the correcting.

7. A computer program product comprising a non-transitory computer-readable medium containing a computer program for adjusting an image positional deviation, the program causing a computer to perform: causing a recording medium to be conveyed; causing a movable body to be moved in a main-scanning direction orthogonal to a conveying direction of the recording medium, the movable body including a recording head to eject a liquid droplet for image recording to the recording medium and being supported movably in the main-scanning direction; causing a plurality of adjustment patterns to be recorded with a predetermined edge interval in the main-scanning direction by causing the liquid droplet ejected from the recording head to land on the recording medium, while causing the movable body to be moved in the main-scanning direction; causing a reading unit mounted on the movable body to read the adjustment patterns by causing the recording medium on which the adjustment patterns are recorded to be irradiated with read light and photoelectrically converting reflected light from the recording medium; calculating a positional deviation correction amount for correcting a deviation of a landing position of the liquid droplet, which is ejected from the recording head and landed on the recording medium, based on an ideal interval between the adjustment patterns recorded on the recording medium and a read result of the adjustment patterns read at the reading; correcting that includes recording the adjustment pattern at a recording position where the interval between the adjustment patterns becomes an integral multiple of a fluctuation cycle in a relative movement of the reading unit and the adjustment pattern, which is caused by movement of the movable body mounted with the reading unit, and correcting the recording position of the adjustment pattern based on the positional deviation correction amount calculated at the calculating; and adjusting an ejection timing of the liquid droplet by the recording head by performing repeatedly at least twice the recording, the reading, the calculating, and the correcting.